In impact type printing mechanisms of the type shown in U.S. Pat. No. 3,742,848 granted to F. E. Huntoon et. al. on July 3, 1973, and U.S. Pat. No. 3,825,103 granted to A. F. Riley on July 23, 1974, an inked ribbon and a paper record medium are squeezed together by the impact of a moving print hammer and a type pallet. The shock from this impact has a tendency to propogate along the length of the paper. The paper record is advanced from a source roll or a fan-fold bin, past the printing station, and over a paperfeed roller. The paper is under slight tension as it passes through the printing station. Paper leaving the feed roller exits through an opening in the printer cabinet and may well continue to be under slight tension as it is pulled into a fan-fold pile or is pulled onto a take-up reel.
The acoustical energy of the shock of each print hammer striking the paper is thus carried along the length of the paper much as voices are carried along a taut string stretched between two paper cups. This impact noise carried outside of the printer cabinet on the paper tends to radiate from the paper since the length of paper extending outside of the printer cabinet radiates acoustical energy somewhat like the cone of a loud speaker and broadcasts this noise into the room.